The present invention relates generally to the operation of small, low-cost DC motors, and more particularly to sensing and switching circuits needed to sequentially power the coils of the motor in synchronism with the movement of the rotor.
Small, low-cost dc motors are used in a large number of low-power and battery operated equipment. For example, such DC motors are often used as motors for continuous operation fans. In such applications the reliability and safety of the equipment is dependent upon the performance and reliability of the fan motor. Such motors are therefore key to the continuous availability of the equipment. An example is a fan in a personal computer. A fan in the body of the computer carries out an essential function by cooling the main processor unit, thereby protecting it from damage caused by overheating. The costs of personal computers have been subject to considerable price erosion, and a low-cost, but highly reliable, fan drive circuit is an essential part of such equipment.
DC motor drives typically contain a magnetic sensitive device for detecting the position of a permanent magnet rotor of the motor, and switching circuitry to switch the voltage from coil to coil to maintain the rotation. However, additional circuit components must usually be present to reduce the radio frequency interference, RFI, generated by the switching process so as to protect the switching and measuring circuits from transients and interference. Further, additional circuitry must be present to supply a suitable voltage power supply to the measurement circuitry and to protect against a reversal of the power supply feed and additional Electro-static discharges, ESD, associated with static build up and handling hazards.